T lymphocytes play an integral role in both the cellular and humoral immune response. Many specific reactions of T lymphocytes are mediated through soluble protein factors. Usually the protein factors present in tissue culture supernatants have been assayed in a limited number of biological systems and described as mediators of particular immunological phenomena. Recently, partially purified supernatants from mixed cell systems or transformed cells have been shown to elicit multiple immunological effects. We have prepared antigen-driven clones of murine T lymphocytes that retain many normal phenotypic characteristics. These cloned cells produce soluble protein factor(s) eliciting the following biological activities: cytolytic T cell amplification, plyclonal B cell stimulation, colony stimulating factor activity, recruitment of Ia+ macrophages into the peritoneal cacity, stimulation of Ia expression by macrphages, stimulation of C4 and C2 production by guinea pig macrophages in vitro, stimulation of expression of Fc receptors, and interferon activity. Gel permeation chromatography using a high-pressure liquid chromatography apparatus of supernatant from a T helper clone produced a 100-fold enrichment of factor(s) with an approximate Mr of 30,000. Also we have derived different cytolytic T lymphocyte clones that respond to these factor(s). This project proposes to characterize biochemically and biologically factor(s) produced by monoclonal murine T lymphocytes, and to attempt to obtain small biologically active peptide fragments through enzymatic degradation of factor(s) to assess the minimum structural requirements for biological activity. Understanding the molecular mechanisms by which these factors elicit their biological effects may afford use the opportunity to modulate specific immune responses in hosts with immunodeficiency, neoplastic, and autoimmune diseases.